General concerns about global warming have initiated many studies in order to find alternative solutions with respect to the utilization of fossil fuels, one of which has been the development of the so-called solid oxide fuel cell (SOFC). Industrial scale production of high power fuel cells remains uncertain essentially due to the high production costs and limited life time of these devices. The high production costs are due to time consuming manufacturing techniques while limited life time is linked to the high working temperature of the cells. Such high working temperatures are necessary in order to achieve high ionic conductivity of the materials used as solid electrolyte as the ionic conductivity is a temperature dependent materials parameter. The main actual trends in research are directed to the developments of solid electrolyte layers with higher ionic conductivity and/or lower thickness in order to be able to reduce the working temperature of the cells. However, the thickness of the solid electrolyte layer has to be chosen with respect to the material quality, in particular, in order to avoid electrical shortcuts (for applications for which such a parameter is important) and/or maintain gas tightness, which are limiting factors, both of which in particular for SOFCs. Further, for low thickness the uniformity of the thickness is highly affected due to the polycrystalline morphology of certain materials commonly used as an electrolyte for the SOFC. The grain size represents a lower limit for the thickness below which the materials properties might change and cannot be guaranteed anymore.
A recent review published in Advances in Manufacturing, vol. 2, Issue 3, pp. 212-221, describes recent efforts obtained using thermal spray techniques and physical vapor deposition (PVD) techniques for SOFC electrolyte layer manufacturing.
For what concerns thermal spraying, developments have been made with regards to the spraying parameters as well as post processing of the deposited layers but none of these developments were able to provide solid electrolyte layers with a thickness below 10 μm nor has been able to achieve high ionic conductivity compared to high quality bulk material, such as, for example, for yttria stabilized zirconia (YSZ).
PVD has normally the advantage that thin films with rather high stoichiometric quality can be produced, but in the context of SOFC the application of PVD is difficult due to the high porosity of the electrode materials acting as growth substrates, which is prerequisite of such cells. This impact on material quality influences the already rather low mechanical stability of such PVD solid electrolyte layers. Similar problems are encountered for other thin film deposition techniques such as, for instance, pulsed laser deposition, see, for instance, Journal of Physics: Conference Series 59, 2007, 140-143. Large area deposition of YSZ films with thicknesses in the range of 300 nm up to 1200 nm have been obtained over areas as large as 50-100 cm2, but such results are only possible on non-porous substrates, for example, Si in the case of YSZ layers deposited by pulsed layer deposition.
The above-mentioned problems apply to all applications that would involve an electrolyte material in solid form and, thus, the present disclosure is not limited to the above-depicted cases. For instance, the present disclosure is also related to oxygen sensors, in particular, like those based on a working principle also called Nernst cell, where a solid electrolyte layer is sandwiched in between two metal electrodes, in particular, made of platinum. The present disclosure could also be applicable to other fields, such as, for instance, Li-ion batteries.
The objective of the disclosure is to propose a fabrication method of a layer of solid electrolyte material, which, is in particular interesting for applications, such as, for instance, electrochemical conversion devices or sensors, in particular a solid oxide fuel cell and oxygen sensors, obviating the above-mentioned detriments. Another objective is to propose a fabrication method of devices and devices comprising such a layer of solid electrolyte. In particular, applications such as, for instance, Li-ion or Na-ion or H-ion batteries, non-oxygen chemical sensors, air separation units, solid oxide electrolyzer cells (SOEC) can be envisaged. Further, another objective is to propose a structure donor substrate that allows multiple transfers of solid electrolyte material.